Tula State University (Tula, Russia)
S. V. Antsiferov, Head of Department, Doctor of Engineering Sciences, Associate Professor, antsser@mail.ru
O. V. Treshcheva, Assistant, Candidate of Engineering Sciences
V. G. Dvoryankin, Associate Professor of Department, Candidate of Engineering Sciences
When constructing underground excavations or tunnels by the closed method near the ground surface in weak soils, the technology of advance support has become widely adopted to prevent processes associated with loss of stability due to the existing lag between the exposure of the excavation surface and the installation of support. Protective screens ensure the stability of the soil mass surrounding the excavation and create conditions for safe work during its driving and support installation, significantly reducing ground surface settlements and thereby helping to preserve the existing surface infrastructure. It is evident that the use of advance ground support affects not only the change in the stress-strain state of the soil, but also the support itself, the consideration of which is essential in the design of excavations. The method for determining the stress state of soil and support in excavations driven by the mining method near the ground surface using advance support in the form of a preinstalled protective screen of pipes is based on rigorous analytical solutions to relevant geomechanical problems. The application of the theoretical concept of interaction between the soil mass, the pipes of the protective screen, and the excavation support – as elements of a single deformable system – has made it possible to reduce the arising geomechanical problems to plane problems of elasticity theory. These consider a semi-infinite medium weakened by a circular hole reinforced with a ring and an arbitrary number of solid washers, which model, respectively, the soil mass, the excavation support, and the cross-sections of the protective screen pipes. The solutions were obtained using the mathematical framework of the theory of functions of a complex variable and the Kolosov-Muskhelishvili potentials, including the analytical continuation of complex potentials for a semi-infinite medium across the boundary of a half-plane into the entire plane, the implications of the Sokhotski-Plemelj theorem, and the properties of Cauchy-type integrals and Laurent series – all of which have demonstrated high efficiency in solving this class of problems. The developed design method has been implemented as a computer program that enables computational experiments to determine the stress state of both the soil mass and the support of excavations with a circular cross-section. The research results are illustrated by calculated stress diagrams (stress plots) showing the stresses that arise in the soil mass along the excavation contour, as well as on the outer and inner contours of the support’s cross-section, under various combinations of the main influencing factors.
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